Bioactive Glass-Ceramic Foam Scaffolds from ‘Inorganic Gel Casting’ and Sinter-Crystallization

Abstract

Highly porous bioactive glass-ceramic scaffolds were effectively fabricated by an inorganic gel casting technique, based on alkali activation and gelification, followed by viscous flow sintering. Glass powders, already known to yield a bioactive sintered glass-ceramic (CEL2) were dispersed in an alkaline solution, with partial dissolution of glass powders. The obtained glass suspensions underwent progressive hardening, by curing at low temperature (40 °C), owing to the formation of a C–S–H (calcium silicate hydrate) gel. As successful direct foaming was achieved by vigorous mechanical stirring of gelified suspensions, comprising also a surfactant. The developed cellular structures were later heat-treated at 900–1000 °C, to form CEL2 glass-ceramic foams, featuring an abundant total porosity (from 60% to 80%) and well-interconnected macro- and micro-sized cells. The developed foams possessed a compressive strength from 2.5 to 5 MPa, which is in the range of human trabecular bone strength. Therefore, CEL2 glass-ceramics can be proposed for bone substitutions.

Extension of the ‘Inorganic Gel Casting’ Process to the Manufacturing of Boro-Alumino-Silicate Glass Foams

“…The X-ray diffraction analysis (although performed with a position sensitive detector, yielding a distinctive high signal-to-noise ratio), shown in Figure 3, clarified only partially the gel nature. Considering that the patterns are nearly identical independently from the state (as received, hardened and fired), we can conclude that the gel was mostly amorphous and in limited quantities, unlike the case of soda-lime glass and other CaO rich glasses [5,14,15,16], for which the shape of typical amorphous ‘halo’ of glasses had significant modifications (i.e., clearly visible 2θ displacements). The pattern of the green sample after NaOH activation actually features some weak peaks consistent with the formation of crystalline N-A-S-H (sodium alumino-silicate hydrated) phases, such as gmelinite (PDF#38-0435), fajausite (PDF#38-0238) and paragonite (PDF#42-0602), although some uncertainties remain, testified by the arrows in Figure 3.…”

“…The proposed approach to cellular glasses is interesting for its inherent flexibility. As evidenced by the experiments with soda-lime glass and bioglass [5,15], the solid content and the duration of both activation and drying stages may affect the viscosity of glass slurries and thus modify the cellular structure in the ‘green’ state. These changes will be the reasonable focus of future investigations, especially at a semi-industrial scale.…”

“…The proposed ‘inorganic gel casting’ process was successfully applied to other glasses, also for the obtainment of glass-ceramic foams [14,15,16]. More precisely, the alkali activation of glass powders was followed by sinter-crystallization, consisting of viscous flow sintering of glass with concurrent crystallization.…”

Influence of Manufacturing Parameters on Mechanical Properties of Porous Materials by Selective Laser Sintering

“…In recent years, due to their exceptional properties, high/medium/low-density porous materials (PMs) with polymeric [1,2,3], ceramic [4,5,6] and metallic [7,8,9,10] matrix, have been widely used in engineering applications. The main mechanical and physical characteristics of PMs (materials with cells, cavities, channels or interstices) vary depending on the pore size, topology, and shape of the pores, as well as the porosity and composition of the solid material [11,12,13].…”

Effect of Phenolic Resin on Micropores Development in Carbon Foam with High Performance

“…High-performance porous material, including metallic foam [1,2,3,4,5,6,7], metallic matrix syntactic foam [8], polymer foam [9,10,11,12], ceramic foam [13,14] and carbon foam [15,16] have attracted great attention during the tremendous growth of industrialization, owing to its excellent properties, such as lightweight, high specific surface area, low density and high strength. Hence, it has been considered as one major promising candidate for applications in environmental protection, vehicles, medicine and aviation industries [1,4,5,16].…”